24 EXPERIMENTAL PHYSIOLOGY 



burn? Reason? Where does the hydrogen burn? Why? 

 After the hydrogen has burned up, examine the sides of 

 the tube. What do you find on them? Why should you 

 expect this? What is oxide of hydrogen? 



C. Hold a fresh test tube full of hydrogen mouth upward 

 for a few moments. At the end of that time test with a 

 match. Is the hydrogen still there? Explain. (Hydro- 

 gen is the lightest substance known.) 



XII. ACIDS, BASES, SALTS, AND NEUTRALIZATION. 



Apparatus. Dilute hydrochloric and nitric acids (one part acid 

 to ten parts water), caustic soda, red and blue litmus paper, evapo- 

 rating dish, glass stirring rod, Bunsen burner. 



Directions. A. Examine some of the dilute hydrochloric 

 acid. What sort of an odor has it? Describe its taste. 

 Rub some between the fingers; describe its "feel." Dip 

 a piece of red litmus into it. What is the effect? i)ip in 

 a piece of blue litmus. Describe the result. (The taste, 

 "feel," and effect on litmus noted are three ways in which 

 you can detect any acid.) Test some common substances 

 and record results; e. g., cream of tartar, vinegar, soda, 

 fruit juices, ammonia. 



B. Dissolve a stick of caustic soda, an .inch long, in a 

 tumbler of water. Examine this liquid. What is its taste? 

 odor? "feel"? Test it with the two kinds of litmus paper 

 and record results. (This kind of substance is called a base. 

 Bases always react in this way to taste, "feel, " and litmus. 

 Certain strong bases are called alkalis.) Test the substances 

 named in A. Which of these are bases? 



C. Pour some of the caustic soda solution into the evap- 

 orating dish. Add, gradually, the dilute hydrochloric acid, 



